Java Lambda Expressions

Lambda Expressions were added in Java 8. They allow you to write shorter, cleaner code, especially when working with collections.

Think of it like a Short Note 📝.

• Instead of writing a full formal letter (Anonymous Inner Class), you just write a quick sticky note (Lambda).
• "Dear Sir, I would like to print this..." vs "Print this."

Syntax

(parameter1, parameter2) -> { code block }

Example: Using Lambda with ArrayList

Before Java 8, printing a list was verbose. Now:

import java.util.ArrayList;

public class Main {
  public static void main(String[] args) {
    ArrayList<Integer> numbers = new ArrayList<Integer>();
    numbers.add(5);
    numbers.add(9);
    numbers.add(8);
    numbers.add(1);

    // Using Lambda Expression
    numbers.forEach( (n) -> { System.out.println(n); } );
  }
}

Storing a Lambda in a Variable

You can store a lambda expression in a variable if the type is a Functional Interface (an interface with only one method). Java provides many built-in ones like Consumer.

import java.util.ArrayList;
import java.util.function.Consumer;

public class Main {
  public static void main(String[] args) {
    ArrayList<Integer> numbers = new ArrayList<Integer>();
    numbers.add(5);
    numbers.add(9);
    numbers.add(8);
    numbers.add(1);

    // Storing lambda in a Consumer interface
    Consumer<Integer> method = (n) -> { System.out.println(n); };

    numbers.forEach(method);
  }
}

Method References

Method references (::) are a shorthand notation of a lambda expression to call a method.

// Lambda
list.forEach(s -> System.out.println(s));

// Method Reference
list.forEach(System.out::println);

There are four types of method references:

1. Static method (Math::max)
2. Instance method of a particular object (System.out::println)
3. Instance method of an arbitrary object of a particular type (String::length)
4. Constructor (ArrayList::new)

Challenge

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